Broach



J. H. G'RACEY May 11, 1948.

BROACH Filed Feb. 28, 1946 4; 4 mwwmmw Q @www Patented May 11, 1948 UNIrs vSTES PATENT OFFICE 3 Claims.

(Granted The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to an improved broach, more particularly 4to an improved broach for riiiing firearm barrels.

In many rearm barrels, particularly pistol barrels, quick twist riing is utilized to impart rapid rotationto the projectile. Likewise a large number of lands are utilized to insure adequate gripping of the projectile so that such projectile will not strip the lands. In rifling `such. a firearm barrel with a broach, such broach is required to perform a large amount of work to produce so many grooves with one pass thereof. Prior art breaching tools have not been very satisfactory when called upon to broach rifle a firearm barrel as above described.

Further, fabrication of prior art broaching tools utilized for one pass 'riiiing of a rearm barrel having a large number of grooves was extremely diicult if the tool was constructed to cut all the grooves simultaneously. due to the combination of the' small diameter of such breaches and the large number of flutes which necessitated a longitudinal flute of extremely narrow width. This produced a broach having insufficient chip clearance resulting in inadequate lubrication and torn rifling unless the length of the broach was made excessive. Consequently it has been a practice to form breaching bits very long, with pairsvof cutters spaced apart thereon a considerable distance, usually without any continuous helical fluting.

Accordingly, it is an object of this invention to provide an improved broach of moderate length for producing a large number of longitudinal grooves in a hollow workpiece, such as riiiing in a rearm barrel, without undue loading of such broach.

Another object of this invention is to provide an improved broach having large width longitudinal helicoidal continuous flutes to facilitate fabrication of such broach and to provide improved chip clearance.

The specific nature of this invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a side elevational view of the broach;

Fig. 2 is a, fragmentary longitudinal section of one end ofthe broachillustrating the oil ducts;

Such was n under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) Fig. 3 is a cross sectional view taken along line 3-3 of Fig. 1;

Fig. 4 is a cross sectional view taken along line 4-4 of Fig. 1;

Fig. 5 is a cross sectional view taken along line 5-5 of Fig. 1;

Fig. 6 is a cross sectional view taken along line 6-6 of Fig. 1;

Fig. 7 is an end viewof the broach; and

Fig. 8 is a fragmentary planiform development of the helical fillets of the tool at the middle part thereof.

Briefly, this invention consists of a broach having a plurality of cutting portions which are virtually separate and complete gang tools, each having cutters for half the whole number of grooves to be cut, and spaced along the same shank. The cutting teeth of each successive portion are angularly displaced relative to the cutting teeth of the preceding portion. However each cutting portion has the same width chip clearance groove. In the case of a riing broach having two cutting portions the cuttingteeth of the second or rear cutting portion are so disposed that grooves cut by such portion will be spaced equidistantly between the grooves produced by the preceding cutting portion. A continuous flute joins the rst portion with the second so that there is an unbroken channel, for ease in ejection of chips and oil along the length of the broach. Such result is accomplished by abruptly changing the twist of the chip clearance flute at approximately the mid-section of the total length of the broach. Thus a chip clearance flute is provided which is as many times wider than the flute of a conventional broach as the number of cutting portions.

The improved broach to be presently described herein is utilized for broach rifling lirearm barrels. Such is -only a specific illustration however, as this invention can readily be embodied in any broach'utilized for producing longitudinally extending grooves in the bore of a hollow workpiece.

In Fig. 1 there is shown a rifling broach 20 fabricated in accordance with this invention. Such broach comprises two cutting portions l and 2 spaced along the broach and separated by an intermediate non-cutting portion I5 comprising fillets of reduced radius, each cutting portion being substantially complete breaches but each having rows of cutting teeth equal to only onehalf of the total number of grooves desired in the workpiece which will in this examplel be assumed tobe eight. 'Each cutting portion I and 3 2 is provided with four longitudinal flutes 3 and intervening fillets, the latter being equally spaced with respect to one another. Flutes 3 and fillets are produced with a, helical lead or twist corresponding to the twist of riliing desired in the firearm barrel. The iiutes extend from the leading end of the^toolthe :length of cutting portion I, whereuponthe -gain or` the lead of the flutesnis abruptly increased for a short distance as shown at II in Fig. l. then assume the same lead or twist provided for portion I which continues to the end of portion2.

Flutes 3 produce continuous flletsfhavingetop faces or lands 5 which extend the whole length of both portions I the same twist as thatof flutes 3, The abrupt change in lead of flutes 3 in portion 4 is provided to angularly displa-ce *lands 5110i -fcut'ting portions l and 2 relatively so 'that llarids` of portion 2 are disposed equidistantly between lands 5 of portion I.

Cutting teeth 5 are formed on the lands-@Stof cutting-portions I andZ 'off broachfZIlfby cutting suitable transverse kerfs in the lands. ESuoh teeth are of conventional construction and need not be further described herein. Landsnmay beA taperedin Vwidth throughoutv the: length of cutting portions I and 2, such landsfbeingfnarrower at the forwarder entering end-thanat the rear or emerging end tofacilitatel .drawing broach 2B- through Athe bore :of f a? firearm barrel (notshown). The portion 4 whichijoinsxcutting portions I4 and 2 isnotprovided with outting teethfas shown in Fig.-.l. .Suchwportionris preferably fofslightly reduced. diameter so that such portion will not :injure the .-bore.

.On the left-or forward end" of portion I,-.as shown vin Fig. L-there `is provided areduced diameter Ybody end `I,and-.a terminal threaded tenon 8 so abroaching machine. Other. conventional means than the one lshown herein :may-be utilized for connecting the .broachto isuchfbroachingma` chine. '-An axial dilatees-provided*irrthefforward end of broach lY-asrshownfin Fig. 1. b. liquelydisposed holes IIJ- extending from duch-9 tothe bottom of flutes 3 are. provided` -toffpermit oil to flow into and along Vflutes-3 Ioffbroach-Z as shown -in Fig.. l.

.In the operation of this tool is pulled throughthe-ffi-rearm.barrel (not shown) by thebroaching machine (not shown) with the forward. left'endof cutting-*portion I entering the bore of ithe firearm barrel first. .l It is obvious Vto one skilled. iny the-.arttha-t vvbroach, 2G mustl be drawn through the-bore. of .theiireJ arm barrel with a helical movement. corresponding 4to the twist. of .landsonbroach l-:Lands 5 of portion l thencut.correspondinggroovesY in the `rearm barrel. Whenlandsf ofportion, 2 enter .thebore of ..the..i=rearml barrel, new grooves Aarey .produced Vwhich areA i spaced Uequidistantly between( .the grooves.produced.-by.: cutting portion I. 'The chips removed byuteethfs drop Ainto flutes.3A where theyfare readily .=forced out by oil introduced underpressure.to1flutese3- through holes I provided,Y .inthev forward part of .broach 2E. As iiutes 3. continue .unbroken alongY the entire length` of the'. broachingstool, such chips are readilywashed out,- thereby.. keeping the broa'chingf tool clear ardfree to,.cut'70` throughout its entire stroke.'

From the 4foregoing description, V 'it' fis. readily apparentthat vthere isy herebyproduceda broachAv that willeasily Iproducea'large'number'cfgrooves g with 'one-pass:l of #such-broach. la'utlren'i'the2 At the end of portion 4 flutes 13E.

and 2. Obviouslyflarids-Eihavethat broach.. 2D. .maybesassembled-sto., 0,

novel construction of this improved broach pro# duces a much stronger broach so that the load placed thereon will not readily fracture such tool. In addition, the large continuous flutes provided on this improved form of broach permit the chips produced by the vcutting action ofteethr to lbe:readily.fforcedf'ouh-.tl:1ereby substantially eliminating anyf.bind.or..tearing due to the non-removal of such chips.

=I claim:

1. A breaching tool for producing longitudinaily extending grooves in the bore of a hollow `-wcmlcpiece comprising, a generally cylindrical body adapted to be insertable in the workpiece and *having 'front land rear cutting portions formedy thereon, a plurality of longitudinally extending rows of radial cutting teeth formed on .said'frontvicuttingxportion in equi-spaced relationship-aboutf-the periphery thereof, each adjacent pair of said rows of cutting teeth defining a longitudinally :extending fchip'-c1earance;groove therebetween, 'Y and a plurality :of extending: rows :of 'cutting teethi formedwonsaid rear cutting portion in equi-spacedrelationship aboutvthe periphery thereof, eac -adjacentfpair of said rows of cutting teeth on-.saidrear` cutting portion defining a longitudinally. extendingrchip olearancegroove therebetweemsaidrows of cutting teeth :onf saidfrear cutting portion:being angularly spaced intermediate saidfrows` -of cutting teeth on said front: cuttingportionsaid body "having'na plurality oigroovesat the 'central portions `thereof -respectively connecting fsaid chipfclearance;grooves=in said front cutting por tion 4with ``said :ich-ip tclearance grooves in said rear lcutting portion.

2. :'A'broaching tool for producing: longitudinally extending: helicalfrgrooves in .the V-loore :of '1a. rearrn barrel comprising, a generally cylindrical bodyradapted AtoA -be insertable' the boreaofi t-he firearm barrel and-having front and 'rear' cutting portions-formed thereon, a pluralitycf longitudinallyfextending helicalrows or radial cutting teethiformed on.-saidffront :cutting portion -in 5 equi-spaced relationship about 7the .periphery improved broach such; 50.

thereof, veach adjacent.v pair of said helical rows of Acutting teeth vdefini-ng a' longitudinally .extending heIicaLohi-p clearance groove therebetween, and -a plurality -of longitudinally extending hel-ical L rows -of Acutting teeth formed on said f rear cutting; portion -inequi-spaced'relationship about the.g periphery thereof; each adacent .pair of said helical rows vof cutting teeth `on--saidrear cutting portion defining alongitudinally extending.i heli- =ca1 chip clearance vgroove '.therebetween, said helical rows -of cuttingteeth on saidfrear-,cutting portionbeing angularlyspaced intermediate said helical rowsiofcutting teethsonsaid front` cutting portion.. saidhelical rows of cuttingteeth on said. rear cutting 'portion having 'the samehelical lead assaid' helical rows of'cutting teeth on said front cutting portion, said body having .a plurality of 'helicalrgrooves of increased leadatL the central portionY thereof respectively connecting saiduhelical 'chip clearance' Agrooves in said front cuttingrlportion' with said'helical 'chip clearance grooves in said rear cutting-portion.

1- 3. s AY broaching tool yfor `producing fslongitudinally extendingggro body. yadapted `to Vbe .insertable-fi-nthe workpiece and having a plurality of cutting portionsforsrned thereon-spaced .alongv the .body .andwsepara-ted .by non-cutting. portions, .a i plurality tof. longitudi- .nallytexten'ding rows of radial` cuttinglt'eeth formed on the foremost cuttingpcrtion'in' equilongitudinally' oves inthe borezof a-hollow. workpiece comprising. a generallyl cylindrical spaced relationship about the periphery thereof, each adjacent pair of said rows of cutting teeth dening a longitudinally extending chip clearance groove therebetween, and a plurality o longitudinally extending rows of cutting teeth formed on each following cutting portion in equispaced relationship about the periphery thereof, each adjacent pair of said rows of cutting teeth on each successive cutting portion defining a longitudinally extending chip clearance groove 10 therebetween, said rows of cutting teeth on each successive cutting portion being angularly spaced intermediate said rows of cutting teeth on the preceding cutting portion, said body having a plurality of grooves at each of said non-cutting 6 portions thereof respectively connecting said chip clearance grooves in each of said cutting portions with said chip clearance grooves inthe next following cutting portion.

JAMES H. GRACE-Y.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,311,584 Allgxunn July 29, 1919 1,744,217 Forberg Jan. 21, 1930 

